NET INCOME (LOSS) PER SHARE - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income (loss)	$ (47,294)	$ 10,618	$ 21,642	$ 13,383
Notes due 2023 interest and financing costs, net	0	430	89	1,006
Adjusted net income (loss)	$ (47,294)	$ 11,048	$ 21,731	$ 14,389
Denominator:
Weighted average common shares outstanding (in shares)	125,603	113,677	124,567	110,951
Employee stock-based awards (in shares)	0	8,326	7,449	8,240
Weighted average common shares outstanding for diluted calculation (in shares)	125,603	130,737	138,910	129,400
Net income (loss) per share, basic (in USD per share)	$ (0.38)	$ 0.09	$ 0.17	$ 0.12
Net income per share, diluted (in USD per share)	$ (0.38)	$ 0.08	$ 0.16	$ 0.11
Convertible Senior Notes Due 2024
Denominator:
Warrants (issued in conjunction with Notes due 2024) (in shares)	0	0	2,641	0
Convertible Notes | Convertible Senior Notes Due 2024
Denominator:
Notes due (in shares)	0	0	3,353	0
Convertible Notes | Convertible Senior Notes Due 2023
Denominator:
Notes due (in shares)	0	8,734	900	10,209